Inflammation is a complex disease involving many factors and cell types. From a disease perspective, many years of research have taught us that inflammatory disorder such as asthma, rheumatoid arthritis, ulcerative colitis, and Cohn's disease and others have a distinct inflammatory cytokine profile. These profiles are the result of the nature of the responding lymphocytes. In other words, inflammation cannot be considered as just “inflammation” but rather that different inflammatory diseases are associated with different secreted cytokines that enhance the proliferation and differentiation of certain sub-populations of T helper cells.
The nature and magnitude of an immune response is largely dictated by the profile of the foreign antigen to which the immune system has been exposed. This event sets into motion a series of events that ultimately leads to the generation of humoral and cell-mediated immunity. These two different effector functions are brought about by the presence of two subpopulations of helper T cells. As also indicated, different inflammatory diseases can be segregated as being either Th1 or Th2, depending on the cytokine profile seen.
Under “normal” healthy conditions there is a delicate balance between pro-inflammatory cytokines typical of Th1 and anti-inflammatory cytokines typical of Th2. If this balance is lost, there will be a polarization resulting in predominantly Th1 or Th2 type inflammation and clinical manifestation of the disease will occur.
Some newer forms of therapeutics now attempt to restore the “in-balance” in for example Th1 type diseases by reducing the cytokine profile of Th1 and thereby allow more of a Th2 profile to occur (Neurath et al, 1995; Mannon et al, 2004). Over the last 5 years or so, many researchers have demonstrated both in vitro and in vivo the validity of the use of oligonucleotides as immunostimulatory agents in immunotherapy applications. The observation that phosphodiester and even modified phosphorothioate oligonucleotides can induce immune stimulation has created a growing interest in developing this effect as a therapeutic tool.
Bacterial DNA has immune stimulatory effects capable of activating B cells and natural killer cells, but vertebrate DNA does not (reviewed in Krieg, 1998, Applied Oligonucleotide Technology, C. A. Stein and A. M. Krieg, (Eds.), John Wiley and Sons, Inc., New York, N.Y., pp. 431-448). It is now understood that these immune stimulatory effects of bacterial DNA are a result of the presence of unmethylated CpG dinucleotides, in particular base contexts (CpG motifs), which are common in bacterial DNA, but methylated and underrepresented in vertebrate DNA (Krieg et al, 1995). The immune stimulatory effects of bacterial DNA can be mimicked with synthetic oligodeoxynucleotides (ODN) containing these CpG motifs. Such CpG ODN have highly stimulatory effects on human and murine leukocytes, inducing B cell proliferation; cytokine and immunoglobulin secretion; natural killer (NK) cell lytic activity and IFN-gamma secretion; and activation of dendritic cells (DCs) and other antigen presenting cells to express costimulatory molecules and secrete cytokines, especially the Th1-like cytokines that are important in promoting the development of Th1-like T cell responses. These immune stimulatory effects of native phosphodiester backbone CpG ODN are highly CpG specific in that the effects are dramatically reduced if the CpG motif is methylated, changed to a GpC, or otherwise eliminated or altered (Krieg et al, 1995 and Hartmann et al, 1999).
In early studies, it was thought that the immune stimulatory CpG motif followed the formula purine-purine-CpG-pyrimidine-pyrimidine (Krieg et al, 1995; Pisetsky, 1996 and Hacker et al., 1998).
Currently there is a significant amount of published data indicating that oligonucleotides containing CpG motifs induce certain cytokines, for example, human and mouse cells respond to CpG motif oligonucleotides by enhanced secretion of interferon-gamma (IFN-gamma) (Iho et al., 1999: Cowdery et al., 1996) IL-1, IL-6, TNF-alpha and IL-12 (Stacey et al., 1996; Jakob et al., 1998 and Sparwasser et al., 1998).
Due to the nature of cytokines induced, CpG containing oligonucleotides are largely considered to induce a Th1 profile both in vitro and in vivo (Zimmermann et al., 1998; Kline, 2000).
In addition to the presence of CpG motifs, researchers have also noted that synthesizing oligonucleotides with a full nuclease-resistant phosphorothioate (PS) backbone can potentate the stimulatory effects of the oligonucleotides, in that these oligonucleotides were much more potent at stimulating B cells, whereas the same sequence with native phosphodiester backbone had no effect (Zhao et al., 1996).
While the presence of a CpG motif within the sequence of an oligonucleotide can induce a strong Th1 cytokine response, this response should be considered in the overall context of the compounds state of chemical modification as well as the general sequence structure.
As already indicated in the background introduction to inflammation, there is a specific cytokine profile that becomes prominent in various types of inflammatory diseases. For example in asthmatic patients there are high levels of IL-4 and low levels of IFN-gamma. This cytokine picture would indicate that asthma is a Th2 type of disease. Rheumatoid arthritis by contrast is better associated with a Th1 type of inflammation characterized in that high levels of IFN-gamma and lower levels of IL-4 are seen.
The phenomenon of corticosteroid resistance has been most extensively studied in asthmatic patients and to a lesser degree in ulcerative colitis where evidence over the years has accumulated, pointing to a number of cytokine abnormalities. Both diseases are classified as Th2 type and interferons as well IL-10 have been implicated as being important factors in the pathogenesis of corticosteroid resistance.
It may be possible that immunostimulatory oligonucleotides that are able to induce endogenous production of such cytokines, such as interferons and IL-10, are able to influence the inflammatory status of setroid resistance or steroid dependent patients in a beneficial manner.
The evidence that certain cytokines can influence the steroid responsiveness is gathered from clinical studies conducted in corticosteroid resistant asthmatic and ulcerative colitis patients who were also all on corticosteroid therapies. In fact, this type of patient subgroup characteristic was the only common denominator between the clinical studies described below.
Interferons (IFNs) play crucial roles in the regulation of a wide variety of innate and adaptive immune responses. Type I interferons (IFN-alpha/beta) are central to the host defense against pathogens such as viruses, whereas type II interferon (IFN-gamma) mainly contributes to the T-cell-mediated regulation of the immune responses (Taniguchi and Takaoka, 2001). Interferons have also found their place in the successful treatment of various human diseases such as benign neoplastic (Gill et al, 1995) and viral diseases (Niederau et al, 1996; Zeuzem et al, 2000).
In a study (Simon et al, 2003), 10 patients with corticosteroid resistant asthma where administered IFN-alpha (3×106 IU/day) (Roferon A® Roche) in addition to the prednisone dose they were all receiving. The trial demonstrated high efficacy in these patients and clinical signs of improvement occurring 1-2 weeks after cytokine therapy, allowing the dose of corticosteroids to be reduced. The authors further noted that the IFN-alpha treatment increased the capacity of peripheral blood T cells to produce IFN-gamma, suggesting there had been a shift from a Th2 type response (typical of asthma and allergic diseases) to a Th1 response.
Moreover, the authors showed that there was also an increase in blood T cells secreting IL-10 in those patients that had received cytokine therapy. As corticosteroids mediate their anti-inflammatory effects, in part, by increasing levels of IL-10, the authors conclude that administration of exogenous IFN-alpha broke the corticosteroid resistance in these patients.
Musch et al (2002) demonstrated a high response rate in corticosteroid refractory ulcerative colitis patients when given IFN-beta i.v. The pilot study enrolled 25 severely ill ulcerative colitis patients proving refractory to basic medication. All patients where on corticosteroids at the time of cytokine treatment. Following treatment, 22 of the 25 (88%) went into remission within 3 weeks with a strong decrease in clinical activity index (CAI) noted 1 week after initiating treatment. The mean length of response was 13 months.
In another study, Sumer et al, (1995), reported an 82% improvement rate to s.c. IFN-alpha cytokine treatment in corticosteroid resistant ulcerative colitis patients. They further noted that the 23 patients responded to the cytokine therapy with a fast improvement (within 15 days) and were in complete clinical and endoscopic remission after 6 months of therapy. Three patients entered remission after longer therapy; however, all 26 patients were observed for more than 2 years without receiving additional therapy and remained in full clinical and endoscopic remission during this period.
Another cytokine that has received interest in the pathogenesis of corticosteroid resistance is IL-10. This cytokine is believed to have potent anti-inflammatory effects in that it can suppress the production of pro-inflammatory cytokines. It also has broad implications in the development of certain inflammatory diseases, most noticeably allergy and asthma (Hawrylowicz et al, 2005), as well as playing a central role in the regulation of immune responses. It is believed that corticosteroids exert their anti-inflammatory effects in part by enhancing IL-10 production (Richards et al, 2005).
Numerous clinical studies have indicated that there is a general lack of sufficient levels of IL-10 in asthmatics which may potentially contribute to a more intensive inflammation. In a randomized double-blind clinical study conducted in children with moderate atopic asthma, Stelmach et al (2002) demonstrated that treatment with Triamcinolone, a corticosteroid, and montelukast, an anti-leukotriene, significantly increased levels of IL-10 in blood serum and in addition significantly improved clinical symptoms.
In another clinical study, levels of IL-10 and IL-10 producing cells were shown to be significantly reduced in patients with severe persistent asthma when compared to mild asthma (Tomitai et al, 2002). These observations were in agreement with previous findings that there is a defect in the production of cells that are able to produce IL-10 in asthmatic subjects (Tormey et al, 1998).
This defect was also shown to exist in corticosteroid resistant asthmatic patients. Under normal conditions, corticosteroids will cause an increased production of IL-10 in corticosteroid sensitive patients. However, Hawrylowicz et al (2002) could confirm that in corticosteroid resistant asthmatic patients, corticosteroids failed to induce IL-10 synthesis. These observations suggest a strong link between induction of IL-10 synthesis and efficacy of corticosteroids.
In a recently published study (Xystrakis et al, 2006), the authors isolated PBMC from corticosteroid resistant asthmatic patients and could demonstrate that addition of vitamin D3 with dexamethasone to these cultures enhanced IL-10 synthesis to levels observed in cells from corticosteroid sensitive patients cultured with dexamethasone alone. Furthermore, and perhaps most significantly, pre-treatment with IL-10 fully restored IL-10 synthesis in these cells in response to dexamethasone.
The use of human bacterial flora to treat gastrointestinal (GI) disorders is not a novel concept, having been practiced periodically for more than 40 years (Eiseman et al, 1958). Significant clinical improvements have been observed in numerous GI disorders including inflammatory bowel disease (IBD) (Bennet and Brinkman 1989). Borody et al, reported in 2003 that human bacteriotherapy could be used to treat severe corticosteroid resistant ulcerative colitis (UC).
In a small study, 6 chronic UC patients who had all previously failed maximum tolerated standard corticosteroid therapies were all given a single fecal enema concomitant to corticosteroid therapies they were currently on. Complete reversal of UC was achieved in all 6 patients following the rectal infusion. The authors also state that all patients ceased anti-inflammatory therapy within 6 weeks and remained in remission in one case for up to 13 years. The apparent success of bacteriotherapy in resistant ulcerative colitis patients may be due to the repopulation of the colon with a “healthy” bacterial flora, but equally as the authors suggest, may also be due to the instillation of a large amount of bacterial DNA, containing abundant CpG motifs, which induced a beneficial immunomodulating effect resulting in complete reversal of the disease.
A study in asthmatics compared the response to a steroid (prednisone) in both steroid resistant and steroid sensitive patients. The patients were first given a “wash-out” period of one week before administration of the steroid. Cytokine profiles before administration and 1 week after indicated that those patients that responded to the steroid moved from a Th2 type to a more Th1 like status. By contrast, those patients that failed to respond to the administered steroid remained Th2 type (Naseer et al., 1997).
While the reason for steroid resistance in asthmatic patients is not entirely clear, numerous studies in humans have indicated that those patients that are resistant to steroids have high persistent levels of IL-2/4 that are not suppressed by the action of steroids. Furthermore, in vitro studies indicate that when IL-2/4 is placed in the culture medium, the cells become resistant to the action of steroids (Sousa A R et al., 2000; Hamid Q A et al., 1999).
In rheumatoid arthritis a similar scenario has been suggested in that steroid resistant patients demonstrate high levels of IL-4, which cannot be reduced when challenged with steroids (Chikanza et al., 2004). Of interest are the findings that IFN-gamma is able to down regulate IL-4 responses (Eui-Young et al., 2000; Smeltz et al., 2002) at the level of transcription.
Steroid resistance or dependence is still a major clinical concern for a large number of patients afflicted with inflammatory diseases as current therapies rely on the use of potent immunomodulators that can induce serious side-effects. A simple straightforward method to enhance steroid efficacy in a steroid unresponsive individual with little risk of unwanted side-effects would essentially improve anti-inflammatory treatment, thus ameliorating the disease in question, and increasing the quality and length of life for a large number of patients.